Fumaric acid esters, i.e., dimethylfumarate (DMF) in combination with salts of ethylhydrogenfumarate, have been used in the treatment of psoriasis for many years. The combination product, marketed under the tradename Fumaderm®, is in the form of oral tablets and is available in two different dosage strengths (Fumaderm® initial and Fumaderm®):
Fumaderm ®Fumaderm ®Fumarate CompoundInitial (mg)(mg)Dimethylfumarate30120Ethyl hydrogen fumarate, calcium salt6787Ethyl hydrogen fumarate, magnesium55saltEthyl hydrogen fumarate, zinc salt33
The two strengths are intended to be applied in an individually based dosing regimen starting with Fumaderm® initial in an escalating dose, and then after, e.g., three weeks of treatment, switching to Fumaderm®. Both Fumaderm® initial and Fumaderm® are enteric coated tablets.
Another marketed composition is Fumaraat 120® containing 120 mg of DMF and 95 mg of calcium monoethyl fumarate (TioFarma, Oud-Beijerland, Netherlands). The pharmacokinetic profile of Fumaraat 120® in healthy subjects is described in Litjens et al., Br. J. Clin. Pharmacol., 2004, vol. 58:4, pp. 429-432. The results show that a single oral dose of Fumaraat 120® is followed by a rise in serum MHF concentration and only negligible concentrations of DMF and fumaric acid is observed. Thus, DMF is thought to be a precursor or prodrug of MHF.
U.S. Pat. Nos. 6,277,882 and 6,355,676 disclose respectively the use of alkyl hydrogen fumarates and the use of certain fumaric acid monoalkyl ester salts for preparing microtablets for treating psoriasis, psoriatic arthritis, neurodermatitis and enteritis regionalis Crohn. U.S. Pat. No. 6,509,376 discloses the use of certain dialkyl fumarates for the preparation of pharmaceutical preparations for use in transplantation medicine or the therapy of autoimmune diseases in the form of microtablets or micropellets. U.S. Pat. No. 4,959,389 discloses compositions containing different salts of fumaric acid monoalkyl esters alone or in combination with a dialkyl fumarate. GB 1,153,927 relates to medical compositions comprising dimethyl maleic anhydride, dimethyl maleate and/or DMF.
Biogen Idec's BG12, an oral dosage form of DMF that is an enteric coated capsule containing DMF in micropellet form, has been in human clinical testing for the treatment of MS and has shown promising results in reducing MS relapses and MS disability progression. Unfortunately, DMF is highly irritating to the skin and mucosal membranes with the result that oral administration of DMF tends to cause serious digestive tract irritation with attendant nausea, vomiting, abdominal pain and diarrhea. This irritation problem is particularly problematic with the mucosal tissue lining the stomach. For this reason, products such as Fumaderm® and BG12 are made with enteric coatings that prevent the DMF from being released from the dosage form until after the dosage form passes out of the stomach and into the small intestine.
More recently, MHF prodrugs including (N,N-Diethylcarbamoyl)methyl methyl (2E)but-2-ene-1,4-dioate and (N,N-Dimethylcarbamoyl)methyl methyl (2E)but-2-ene-1,4-dioate are disclosed in Gangakhedkar et al. U.S. Pat. No. 8,148,414. Additional MHF prodrugs are disclosed in Cundy et al. U.S. Patent Application 61/595,835 filed Feb. 7, 2012. Both of these disclose the use of MHF prodrugs for treating a number of medical conditions, including MS and psoriasis.